The present invention relates to a read/write arrangement for Contact Probe Storage (CPS) arrangements and the like, wherein a heater is used to heat a medium and modify its topography so that data bits are written thereinto, and wherein a read sensor arrangement, which is based on a FET (Field Effect Transistor), responds to changes in distance from a substrate that supports the medium and emits an electric field, induced by the modified topography.
It has been hitherto been proposed to sense data which is written onto a movable medium using a probe that is supported on a cantilever and used to contact movable the medium. A heated element (heater) is provided in the cantilever proximate the probe. The heater is heated by passing a current of electricity therethrough. By using heat transfer characteristics between the movable medium and the probe (or a portion of the cantilever in which the heating element is formed), it is possible to determine minute changes in distance between the movable medium and the cantilever on which the probe is carried, and to use this as a means for reading out the data stored on the movable medium.
The heater in the cantilever can be used for both reading and writing. The reading function uses a thermal readback sensor arrangement which exploits a temperature-dependent resistance function. In this arrangement, the resistance (R) increases nonlinearly with heating power/temperature from room temperature to a peak value of 500-700° C. (writing). The peak temperature is determined by the doping concentration in the heater platform, which ranges from 1×1017 to 2×1018. Above the peak temperature, the resistance drops as the number of intrinsic carriers increases because of thermal excitation.
During sensing, the resistor is operated at about 200° C. This temperature is not high enough to soften the polymer medium, as is necessary for writing, but allows molecular energy transfer between the cantilever on which the probe is carried, and the moving medium, to remove heat and thus provide a parameter which allows the distance between the cantilever on which the probe is carried and the medium on which the probe is running to be measured.
That is to say, this thermal sensing is based on the fact that the thermal conductance between the heater platform and the storage substrate changes according to the distance between them. The medium between a cantilever and the storage substrate, in this case air, transports heat from one side the heater/cantilever to the other of storage media/substrate. When the distance between heater and media is reduced as the probe moves into a bit indentation, heat is more efficiently transported through the air and the heater's temperature and hence its resistance decreases. Thus, changes in temperature of the continuously heated resistor are monitored while the cantilever is scanned over data bits, providing a means of detecting the bits.
Under typical operating conditions, the sensitivity of the thermomechanical sensing is even better than that of piezoresistive-strain sensing inasmuch as thermal effects in semiconductors are stronger than strain effects. A ΔR/R sensitivity of about 10−4 /nm is demonstrated by the images of the 40-nm-size bit indentations. This is better than the results are obtained using the piezoresistive-strain technique.
Nevertheless, the thermal response has been found to be slower than desired and is significantly slower than the cantilever's ability to mechanically follow the data pattern written in the medium. This leads to the system's read performance being slower than it would be if it were not limited to the thermal response of the sensing system.